This application relates to methods and systems for cryogenic cooling. “Cryogenic cooling” refers generally to processes that use liquefied gases, i.e. “cryogens,” in providing the cooling, which may take the form of freezing or simply chilling a system or material.
There are numerous applications, both medical and nonmedical, in which it is desirable to provide effective cooling. Any cooling process may be considered as involving one or more of four basic processes that result in removal of a heat load: evaporation, conduction, radiation, and convection. One challenge that is presented in cryogenic cooling techniques results from the process of evaporation, and may be understood by considering cooling within a small channel. The process of evaporation of a liquefied gas results in enormous expansion as the liquid converts to a gas; the volume expansion is on the order of a factor of 200. In a small-diameter system, this degree of expansion consistently results in a phenomenon known in the art as “vapor lock.” The phenomenon is exemplified by the flow of a cryogen in a thin-diameter tube, such as is commonly provided in a cryoprobe. A relatively massive volume of expanding gas that forms ahead of it impedes the flow of the liquid cryogen. Traditional techniques that have been used to avoid vapor lock have included restrictions on the diameter of the tube, requiring that it be sufficiently large to accommodate the evaporative effects that lead to vapor lock. Other complex cryoprobe and tubing configurations have been used to “vent” N2 gas as it formed along transport tubing. These designs also contributed to limiting the cost efficacy and probe diameter.
There is accordingly a general need in the art for improved methods and systems for providing cryogenic cooling.